Conventionally, photolithographic technology has been used in forming microelements or carrying out a fine processing in a variety of fields, for example, in production of semiconductor integrated circuits such as LSIs, display screens of FDPs, circuit boards for thermal heads, and others. Positive- or negative-working photosensitive resin compositions have been used for forming resist patterns in the photolithographic technology. Among these photosensitive resin compositions, positive-working photosensitive resin compositions containing an alkali soluble resin together with a quinonediazide compound as a photosensitive agent have been used widely. Various kind of such compositions were described as “novolak resin/quinonediazide compounds” in a large number of literatures, for example, including Japanese Patent Application Publication (JP-B) Nos. 54-23570 and 56-30850 and Japanese Patent Application Laid-Open (JP-A) Nos. 55-73045 and 61-205933. Research and developments on these compositions containing a novolak resin and a quinonediazide compound have been carried out from both aspects of the novolak resins and photosensitive agents.
On the other hand, in the fields demanding a thick film processing such as magnetic head and bump, it is necessary to form a resist pattern having a high-aspect ratio and perpendicular wall. However, the conventional photoresists described above have problems, for example, of insufficient resolution or sensitivity, inability to produce desirable resist patterns, and the like, because of deterioration in light transmission of the films associated with increase in thickness; and thus there exists a need for a new photoresist that can overcome the problems.
As dry-film-system photosensitive resin compositions that can form a thick resist pattern, there have been hitherto known a photosensitive resin composition comprising a novolak resin, an acetal compound having repeating acetal units in the main chain wherein each a-carbon atom of the alcohol component of the acetal units is aliphatic, and an acid generator (JP-A No. 53-133429); a photosensitive resin composition comprising an alkali soluble resin such as novolak resin, an acetal compound, an acid generator, and additionally a particular additive such as an alkyl acrylate (JP-A No. 57-37349); and a photosensitive resin composition comprising an alkali soluble resin such as novolak resin, an acetal compound, and an acid generator (JP-A No. 58-114031). Further, as the photosensitive resin compositions comprising an acetal compound and an acid generator, known are a photosensitive resin composition comprising a novolak resin prepared using three different phenols, an acetal compound, and an acid generator (JP-A No. 62-124556); a photosensitive composition comprising a novolak resin having an acetal bond in the molecule and an acid generator (JP-A No. 62-215947); and a photoresist comprising a novolak resin, an acetal compound (chlorobenzaldehyde-diphenoxyethylacetal), and an acid generator (2-alkoxyphenyl-4,6-bis(trichloromethyl)-s-triazine) (JP-A No. 4-182650). Furthermore, there are indicated a photosensitive resin composition comprising a polymer having an acid-dissociative functional group, a polyvinyl lower alkyl ether, and an acid generator (JP-A No. 2001-281863) as the photosensitive resin composition for forming an ultra-thick film resist having a thickness of 20 μm or more that are suitable for forming a bump; and a photosensitive resin composition comprising an acid generator and an alkali soluble novolak resin of which a part of the hydrogen atoms of the phenolic hydroxyl groups are substituted with a 1,2-naphthoquinone-diazido-sulfonyl group (JP-A No. 2001-312060) as the photosensitive resin composition compatible with the thick resists having a thickness of 3 μm or more that are suitable for producing a magnetic head. However, for making the composition more compatible with an ultra-thick film, for example, having a thickness of 20 to 100 μm, there exist needs currently, for example, for improvement of the resolution thereof for production of minute rectangular patterns having a high aspect ratio, good pattern reproducibility, improvement of the heat resistance of the pattern obtained, and improvement of the throughput (yield per unit time) during production for reduction in production cost, thus demanding further improvement of the photosensitive resin composition currently.
Under the circumstances described above, an object of the present invention is to provide a chemically amplified positive-working photosensitive resin composition compatible with a thick film processing and an ultra-thick film processing that has high sensitivity and high film retention ratio (after development), excellent in coating properties, capable of forming favorable high-resolution patterns, and also excellent in the heat resistance of the patterns obtained.
Another object of the present invention is to provide a chemically amplified positive-working photosensitive resin composition for use in the electrolytic gold-, copper-, nickel- or solder-plating step of the semiconductor packaging technology.